Plot data and satellite imagery were used to examine changes in vegetation between 2000 and 2007. These data were examined in light of changes in rabbit numbers (data owned by and provided to us from Parks and Wildlife Tasmania).

Methods and data

Vegetation Change. Kate Kiefer established 18 relatively homogenous plots of 25 m2 in a range of ... vegetation types between November and March 2001. Individual plant species cover was visually calculated within five random 1m2 quadrats within each site and mean values determined. Dana Bergstrom, Kate Kiefer, Jane Wasley and Arko Lucieer re-sampled the same sites in April 2007. The data matrix consisted of 18 sites, 34 taxa and temporally separated sampling intervals: 2001 and 2007. Species also included collective categories for leafy bryophytes, lichens, bare ground and dead vegetation. At each site altitude, slope, aspect, a subjective estimate of the wind exposure and the degree of waterlogging were also recorded. The data matrix of sites and mean cover for the site (mean of cover from 5 x 1 m2 quadrats) is provided. Also in the data matrix is GPS location of the site which is recorded for each star picket that marks each site on the island. Site code consist of site number (first two numerals) - year 01 or 07 (2001 or 2007). The data matrix also includes some site information: a subjective exponential soil-water scale (1- 5: dry - wet); a subjective exponential site exposure scale (1-5: sheltered to exposed); slope, altitude, aspect and mean substrate depth (mean of three random probes across the site) (Data Table 1). Changes at the site and rabbit activity are summarised in Data Table 2.

Remote Sensing Imagery. Information on changes in vegetation communities were scaled up to whole-island level using satellite imagery. We used Landsat ETM+ imagery acquired on 12 December 2000 and Quickbird imagery acquired on 15 March 2007 to detect changes in vegetation cover on Macquarie Island. The Quickbird image with its 2.4 m pixel size was resampled (by pixel averaging) to the 25 m Landsat pixel size to compare the images at the same resolution. The images were orthorectified to correct terrain and geometric distortions. Radiometric, illumination, and atmospheric differences were also corrected. These corrections are crucial for change detection algorithms as false changes are often introduced by geometric offsets and shadowing effects. Multispectral bands 1 (blue), 2 (green), 3 (red), and 4 (near-infrared (NIR)) of both images were used for change detection.